The U.S. ambassador to Ukraine has accused the country’s Prosecutor-General’s Office of obstructing efforts to combat corruption and shielding its own employees from graft investigations.

Western governments supporting Ukraine’s reform agenda have repeatedly stressed the need for Kyiv to tackle endemic corruption. But the comments by Ambassador Geoffrey Pyatt were unusually blunt for a U.S. official speaking before the public.

Pyatt told a group of business executives and investors in Odesa that the Prosecutor-General’s Office is an “obstacle” to anticorruption reforms by failing to “successfully fight internal corruption."

“Rather than supporting Ukraine’s reforms and working to root out corruption, corrupt actors within the Prosecutor-General’s Office are making things worse by openly and aggressively undermining reform,” Pyatt said in the September 24 speech.

“They intimidate and obstruct the efforts of those working honestly on reform initiatives within that same office,” Pyatt said. “The United States stands behind those who challenge these bad actors."

There was no immediate reaction to Pyatt's comments, either by the Prosecutor-General’s Office or by the government of President Petro Poroshenko.

He called for an investigation of officials within the Prosecutor-General’s Office who he says stymied efforts to pursue tens of millions of dollars in “illicit assets” that former Ukrainian official Mykola Zlochevskiy held in Britain.

Zlochevskiy served as environment and natural resources minister under former President Viktor Yanukovych, a Kremlin ally whose ouster amid mass street protests in 2014 triggered events that led to Russia’s annexation of Ukraine’s Crimean Peninsula and a bloody war with Russian-backed separatists in eastern Ukraine.

Pyatt said that “those responsible for subverting the case” against Zlochevskiy “should -- at a minimum -- be summarily terminated.”

Since his appointment by Poroshenko in February, Prosecutor-General Viktor Shokin has faced accusations of stalling high-profile corruption cases against allies of Yanukovych.

Shokin signed a decree on September 22 establishing a special anticorruption department within the Prosecutor-General’s Office.

Pyatt urged the audience to “speak up in support of these brave investigators and prosecutors” leading this department, who “have delivered important arrests and have sent the signal that those who abuse their official positions as prosecutors will be investigated and prosecuted.”

“Give them the resources and support to successfully prosecute these and future cases,” he said.

The Black Sea port of Odesa, where Pyatt spoke, is a notorious hub for crime and drug trafficking and has come under additional pressure with the arrival of Ukrainians displaced by war to the east.

It is the main city in the Odesa region, which is led by Mikheil Saakashvili, the former president of Georgia who was named governor by Poroshenko in May.

Earlier this month, Saakashvili accused officials in Kyiv of sabotaging his attempts to enact the kind of sweeping reforms, including a harsh crackdown on corruption, that he is widely credited with conducting during his presidency in Georgia.

Pyatt said Odesa’s “vision for reform is transformative.”

“If successful, Odesa can be a model of transparent, accountable government and business,” he said.

Ukraine is near the bottom of global rankings of corrupt nations, according to Transparency International. The German-based advocacy group last December called Ukraine “still the most corrupt country in Europe.”